Low blood pressure, or hypotension, occurs when the force of blood against the artery walls is unusually low. While mild hypotension is often a sign of good health, it can become a serious problem. Low blood pressure can be fatal, but only when it drops suddenly and severely enough to cause circulatory shock. Chronic, mild hypotension, which may cause occasional dizziness, rarely poses a threat to life.
When Low Blood Pressure Becomes Dangerous
Low blood pressure is generally defined as a reading below 90 millimeters of mercury (mmHg) systolic and 60 mmHg diastolic (90/60 mmHg). This number alone is not the sole measure of danger, as many healthy individuals naturally maintain pressures in this range without symptoms. Danger arises when blood pressure drops acutely and dramatically. This drop can happen to a person with a normal reading or someone who already has chronic low blood pressure.
A sudden decline in systolic pressure of 30 to 40 points from a person’s typical baseline is often considered a critical threshold. The seriousness is determined by the rate of the drop and the presence of symptoms. These symptoms indicate the body can no longer compensate for the reduced pressure. When pressure is too low, the circulatory system cannot effectively deliver oxygen to the body’s tissues, signaling a medical emergency.
The Physiological Mechanism of Circulatory Shock
The fatal outcome of severe hypotension results from inadequate blood flow to the body’s tissues, a state known as hypoperfusion. This failure of circulation defines circulatory shock, where cells are deprived of necessary oxygen and nutrients. Without sufficient oxygen, cells switch to anaerobic metabolism, which rapidly produces lactic acid and changes the internal cellular environment.
Oxygen deprivation leads to widespread cellular damage and ultimately cell death across vital organ systems. The brain, kidneys, and heart are particularly vulnerable to this lack of perfusion. This results in mental status changes, decreased urine output, and damage to the heart muscle. As cellular function deteriorates, the body enters a vicious cycle where the circulatory system fails, leading to multi-organ failure and death if not immediately reversed.
Acute Health Events That Trigger Severe Hypotension
A sudden and severe drop in blood pressure is typically triggered by a major acute health event that overwhelms the body’s compensatory mechanisms. One common cause is hypovolemic shock, which results from a massive loss of blood volume, such as from severe trauma, internal bleeding, or extreme dehydration. When less fluid is circulating, the pressure inside the vessels drops precipitously.
Several acute health events can lead to severe hypotension:
- Hypovolemic shock results from massive loss of blood volume (e.g., severe trauma or dehydration).
- Septic shock is a complication of severe infection where bacterial toxins cause widespread dilation of blood vessels, reducing vascular resistance.
- Cardiogenic shock occurs when the heart muscle is damaged (e.g., during a heart attack) and can no longer pump blood effectively.
- Anaphylaxis involves life-threatening allergic reactions that cause sudden, massive vasodilation and fluid leakage from blood vessels.
Recognizing Symptoms That Require Emergency Care
The symptoms of severe hypotension indicate a state of shock that requires immediate medical intervention. These symptoms are directly related to the body’s organs not receiving enough blood flow. A person experiencing this emergency may exhibit confusion or an altered mental state, especially in older adults, due to insufficient oxygen reaching the brain.
The skin often becomes cold, pale, and clammy as the body redirects blood flow away from the extremities to protect the core organs. Rapid, shallow breathing and a weak but fast pulse are common signs as the heart attempts to compensate for the low pressure. Fainting or the inability to stand indicates the brain has been critically deprived of blood. If any of these severe signs occur, such as sudden weakness, confusion, or loss of consciousness, emergency services should be called immediately.